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324

PRACTICAL ORGANIC CHEMISTRY

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and give off water or (if nitrogen is present) ammonia or basic
constituents. But a great number of common organic com-
pounds are volatile without decomposition.
The Elements.Test for nitrogen,1 sulphur, and halogens. If
none of these are found, carbon and hydrogen are present and, if
the substance has given off water or is soluble in water, it may
be assumed that oxygen is present as well. The action of sodium
on the substance, if liquid, or on its solution in benzene orligroin,
if solid, should be tried in the apparatus, Fig. 86, and the gas
evolved ' tested for hydrogen, which if present, may indicate
hydroxyl, ketone, or ester groups.
The presence of nitrogen may indicate an ammonium salt,
organic base (aniinc or alkaloid], amino-acid, amide, cyanide,
\sotyanide, oxime, nitroso- or nitro-compound, azo-compound, etc.
The presence of sulphur may indicate a sulphate of an organic
base, alky I sulphate, sulphite, sulphide, tnercaptan, sulphonic acid,
bisulphite compound of aldehyde or ketone.
The presence of a halogen may indicate a haloid salt of a
base, alky-l, alkylene, or aryl haiide, add haiide, haloid derivative
of an. aldehyde or acid. Some substances, like mustard oils,
amino-sitlphonic acids and thioamides, contain both nitrogen
and sulphur.
Solubility.Try if the substance dissolves in hot or cold
water. Apart from the salts of organic bases and acids, many of
which are very soluble in water, the solubility of simple organic
substances is generally determined by the presence of the OH
group (including CO.OH and SO2.OH groups) and to some
extent by the NH2 group. The greater the proportion of OH
groups to carbon, the greater, as a rule, is the solubility in water.
The lower alcohols, methyl, ethyl and propyl alcohols, are
miscible with water; normal butyl and wvbutyl alcohols (fermenta-
tion) dissolve in about 10 parts of water at the ordinary tempera-
ture ; amyl alcohol (fermentation) in about 40 parts of water, The
first two may be separated from solution by the addition of solid
potassium carbonate. The addition of common salt is sufficient to
1 It is sometimes difficult to detect nitrogen by the sodium test. The result should
not be regarded as conclusive, especially if the substance is volatile, unless it has
been dropped in small quantities at a time into the melted metal, which should _be
heated in a hard-glass tube clamped in a retort-stand. Special care must be used with
mtro-compounds, which may explode and shatter the tube.